The present invention relates to an audio-band electromechanical vibration converter in which a low-band electric signal causes a body-felt vibration and thereby makes it possible to appreciate double bass sound through ear drum vibration and body-felt vibration.
The lower the frequency of sound is below 150 Hz, the greater will be the proportion of sound which is felt not only as a vibration of ear drum but also as a sound pressure, i.e., air vibration felt by the body. The so-called double bass sound is felt as an air vibration which must be appreciated not only through the ear but also through the skin or body; a true appreciation of double bass sound is possible only when audio sensation is coupled with body sensation.
For ideal appreciation of double bass sound, an attempt has been made at causing a body-felt vibration synchronized with an electric signal to drive the speaker.
For instance, U.S. Pat. No. 3,366,749 discloses an audio-band electromechanical vibration converter to cause a body-felt vibration, in which a gap is formed by a yoke with a magnetic pole; a frame-wound coil is set in said gap; and a vibration is caused through magnetic interference between the magnetic force developed in said coil by an electric signal and the magnetic force of said magnetic pole. In this case a screw stem is erected on the coil frame and the coil frame is supported through a damper on the yoke in such a manner that said coil frame and said yoke can be displaced relative to each other. Thereby, since the coil frame is supported at a position deviated from the gap in which the coil is set, the coil set in the gap after fitted to the vibration plate by said screw stem is liable to be shifted in position under the load of said yoke, resulting in a failure to cause an effective vibration. It is conceivable to make the damper rigid enough to stand the load of the yoke so that the coil may be properly positioned in the gap, at whatever angle the casing is attached; in that case, however, it would be impossible to cause a satisfactory vibration of double bass. On the contrary, if the damper were made soft enough to cause a satisfactory vibration of double bass, the coil would not be properly positioned in the gap on account of the load of the yoke, thereby making the action unstable.
Moreover, since the coil frame is attached to the vibration plate by means of said screw stem erected thereon, with the thickness increased, the whole assembly becomes inevitably bulky.
In the case of a converter being attached to a vibration plate embedded in a chair from the backside of said chair, as disclosed in U.S. Pat. No. 3,366,749, said converter may be employed without any trouble, but in this case it will be necessary to modify the whole structure of the chair. If an assembly of such a converter attached to an independent vibration plate without modification of chair structure is applied to a chair, the thickness will be increased and the user of the chair will feel discomfort.
The present invention, free from the above-mentioned troubles, is characterized in that a yoke having a permanent magnet and a magnetic gap is displaceably set through a damper in a casing and said casing can produce a mechanical vibration synchronized with a low-band audio signal, without increasing the thickness of the whole assembly.